The present invention is concerned with a novel process for the manufacture of a .gamma.-halotiglic aldehyde and with the use of the thus-manufactured .gamma.-halotiglic aldehyde for the production of .gamma.-acetoxy-tiglic aldehyde or of certain C.sub.5 -Wittig aldehyde halides. These products are known, important intermediates for the manufacture of various apocarotenals and diapocarotenals as well as of vitamin A.
.gamma.-Chlorotiglic aldehyde and the corresponding .gamma.-bromo compound are known and can be manufactured according to a number of known methods starting from methylglyoxal dimethyl acetal [see Belgian Patent 633,007, German Offenlegungsschriften (DOS) 1,188,577 and 1,952,649 as well as Finn. Chem. Lett. 1984, 102 et seq.], from isoprene [DOS 2,620,968, U.S. Pat. No. 4,288,635, J. Org. Chem. 41, 1648 et seq. (1976), Rec. Trav. Chim. Pays-Bas 99, 384 et seq. (1980) as well as Tetrahedron 34, 2205 et seq. (1978)], from 3-methyl-2-butenyl chloride [Nippon Kagaku Kaishi 1975, 2246 et seq./Chem. Abs. 84(9), 58575s], from tiglic aldehyde [Tetr. Lett. 20, 1719 et seq. (1973)] or from 1-methoxy/ethoxy-2-methyl-1,3-butadiene [J. Gen. Chem. USSR 32, 1088 et seq. (1962; English translation), Russian Chem. Rev. 38, 237 et seq. (1969), Pure & Appl. Chem. 47, 173 et seq. (1976), J. Gen. Chem. USSR 32, 3105 et seq. (1961; English translation) as well as Helv. Chim Acta 54, 1369 et seq. (1971)]. With respect to the last-mentioned method, the 1-alkoxy-2-methyl-1,3-butadiene can be bromoalkoxylated using N-bromosuccinimide in methanol or ethanol to give the corresponding .gamma.-bromotiglic aldehyde dialkyl acetal, from which in turn there can be produced as required the corresponding .gamma.-acetoxy-tiglic aldehyde acetal and subsequently .gamma.-acetoxy-tiglic aldehyde or .gamma.-bromotiglic aldehyde. From the respective scientific literature it is not evident that brominating agents other than N-bromosuccinimide have been used for the manufacture of .gamma.-bromotiglic aldehyde from the 1-alkoxy-2-methyl-1,3-butadiene. Further, the manufacture of .gamma.-chlorotiglic aldehyde starting from this 1,3-butadiene derivative by haloalkoxylation is also not known from the scientific literature. However, it can be expected that the corresponding N-chloro compound, i.e. N-chlorosuccinimide, could be used instead of N-bromosuccinimide for this purpose and in an analogous manner.